1. Field of the Invention
This invention relates generally to oil well production and, in particular, to a method for separating oil and water below the surface of the ground so that only oil is produced at the surface with the water being separately conveyed through the well bore and discharged into a disposal formation without raising it to the surface of the well.
2. Description of the Prior Art
Oil and/or gas wells quite often pass through productive strata whose yield, besides including oil, gas and other valuable products, also includes undesirable and unwanted heavy precipitates such as salt water. In oil well production operations, relatively large quantities of water are frequently produced along with the valuable products. This is particularly true during the latter stages of the producing life of a well. Handling this water represents a significant expense in lifting, separation and disposal.
Various methods have been employed for extracting the valuable yield from the heavier and unwanted precipitates such as salt water. Some have involved the pumping of the total yield to the surface of the well and then using various methods for separating the valuable yield from the unwanted portion of the yield. In addition, the unwanted portion of the yield, after having been pumped to the top of the well and separated, has been pumped downwardly again through a remote well bore into a disposal stratum.
In some oil wells the unwanted heavier precipitate can amount to as much as eighty percent to ninety percent of the total yield and, accordingly, in order to obtain a given volume of valuable yield from the well, eight or nine times the volume of the valuable yield must first be pumped to the surface of the well and then the valuable yield must be separated from the unwanted portion of the yield. As previously set forth, this process can be very slow and expensive. Although the problem of producing waterfree oil from a reservoir may occur at any stage in the life of an oil well, the proportion of water to valuable yield generally increases with time as the oil reserves decline. Ultimately, when the lifting costs of the combined oil and water exceed the value of the recovered oil, abandonment becomes the only reasonable alternative. As production nears this stage, the local area of the oil field is considered as being exhausted and the well is referred to as being a "stripper".
Many procedures have been tried for producing waterfree oil from a formation which includes a large quantity of water. For example, the oil and water produced are pumped or otherwise flowed together to the surface where they are treated to separate the oil from the water. Since the volume of the water is usually much greater than that of the oil, the separator must handle large volumes of water and, therefore, must be large and, accordingly, relatively expensive. Moreover, the water produced contains mineral salts which are extremely corrosive, particularly in the presence of air. Also, flowing of the oil and water together upwardly through the well sometimes results in emulsions forming which are difficult to break. Such emulsions frequently must be heated in order to separate them even in the presence of emulsion treating chemicals. The heating of the large amount of water, as well as the small amount of oil, requires an expenditure of large amounts of energy to reduce the net equivalent BTU production from the well.
Water produced from deep formations within the earth frequently contains large amounts of natural salts. For this reason, the produced salt water cannot be disposed of by allowing it to flow into surface drains or waterways. Relatively small volumes of salt water can sometimes be disposed of by drainage into a slush pit or evaporation tank. However, the required disposal method for large volumes of salt water is to introduce the water into a subsurface formation where no damage can result. This requires that a disposal well be provided for receiving the produced salt water. By returning the water to the same formation in this manner, the water is disposed of and also acts more or less as a repressurizing medium to aid in maintaining the bottom hole pressure and in driving the well fluids toward the producing well. In those areas where producing wells are widely separated, the cost of drilling disposal wells for each producing well is prohibitive. In such instances, it is necessary to lay a costly pipeline gathering network to bring all of the produced water to a central location, or alternatively, to transport the produced water by trucks or similar vehicles. Regardless of the method for transporting the waste salt water from the producing well to the disposal well, the cost of the disposal can be, and usually is, prohibitive.